Sherman cites studies of the vocabulary in Iris Murdoch’s later works, which showed signs of Alzheimer’s years before her diagnosis.
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Rambling and long-winded anecdotes could be an early sign of Alzheimer’s disease, according to research that suggests subtle changes in speech style occur years before the more serious mental decline takes hold.

The scientists behind the work said it may be possible to detect these changes and predict if someone is at risk more than a decade before meeting the threshold for an Alzheimer’s diagnosis.

Janet Cohen Sherman, clinical director of the Psychology Assessment Center at Massachusetts General Hospital, said: “One of the greatest challenges right now in terms of Alzheimer’s disease is to detect changes very early on when they are still very subtle and to distinguish them from changes we know occur with normal ageing.”

Speaking at the American Association for the Advancement of Science in Boston, Sherman outlined new findings that revealed distinctive language deficits in people with mild cognitive impairment (MCI), a precursor to dementia.

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“Many of the studies to date have looked at changes in memory, but we also know changes occur in language,” she said. “I’d hope in the next five years we’d have a new linguistic test.”

Sherman cites studies of the vocabulary in Iris Murdoch’s later works, which showed signs of Alzheimer’s years before her diagnosis, and the increasingly repetitive and vague phrasing in Agatha Christie’s final novels – although the crime writer was never diagnosed with dementia. Another study, based on White House press conference transcripts, found striking changes in Ronald Reagan’s speech over the course of his presidency, while George HW Bush, who was a similar age when president, showed no such decline.

“Ronald Reagan started to have a decline in the number of unique words with repetitions of statements over time,” said Sherman. “[He] started using more fillers, more empty phrases, like ‘thing’ or ‘something’ or things like ‘basically’ or ‘actually’ or ‘well’.”

Worsening “mental imprecision” was the key, rather than people simply being verbose, however. “Many individuals may be long-winded, that’s not a concern,” said Sherman.

Sherman and colleagues had initially set out to test the “regression hypothesis”, the idea that language is lost in a reverse trajectory to how it was acquired during childhood, with sophisticated vocabulary being the first thing to go.

The hypothesis turned out to be wrong, but the team did find that dementia is accompanied by characteristic language deficits. In a study, the scientists compared the language abilities of 22 healthy young individuals, 24 healthy older individuals and 22 people with MCI.

When given an exercise in which they had to join up three words, for instance “pen”, “ink” and “paper”, the healthy volunteers typically joined the three in a simple sentence, while the MCI group gave circuitous accounts of going to the shop and buying a pen.

“They were much less concise in conveying information, the sentences they produced were much longer, they had a hard time staying on point and I guess you could say they were much more roundabout in getting their point across,” said Sherman. “It was a very significant difference.”

In another test, people were asked to repeat phrases read out by the investigator. Complex vocabulary or grammar was not a problem, but those with MCI appeared to have a mental block when they were given phrases involving ambiguous pronouns, such as “Fred visited Bob after his graduation”, which the scientists said required more mental agility to assign a meaning.

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The prospect of an effective treatment for Alzheimer’s has had knockbacks in the past year as a string of drugs designed to sweep away the amyloid plaques seen in the brains of patients have each been shown to make no difference to the rate of cognitive decline in trials. Between 2002 and 2012, 99.6% of drugs studies aimed at preventing, curing or improving Alzheimer’s symptoms were either halted or discontinued.

Some believe that these failures may be, in part, because by the time Alzheimer’s is diagnosed, the disease has already caused irreparable damage to the brain, making it too late for treatment to help.

“So we are trying to push the detection period back to the very subtle, early changes in in Alzheimer’s disease,” said Sherman.

There are 850,000 people with dementia in Britain and this figure is expected to reach 1 million by 2025. Last year, dementia overtook heart disease as the leading cause of death in England and Wales.